Refrigeration



March 23, 1943..

W. JONES REFRIGERATION Filed Jun e 20, 1940 2 Sheets-Sheet 1 Snventor(Ittorneg March 23, 1943. w; JONES REFRIGERATION Filed June 20, 1940 2Sheets-Sheet 2 "1uIllIIII II IIIIIIIIIIIIIIIllllllllllllllllllllllllllllIlllll w 5 d I Srmentor Bu Z I i1 GttomegPatented Mar. 23, 1943 REFRIGERATION Walter Jones, Princeton, N. 3.,assignor to Carrier Corporation, Syracuse, N. Y., a corporation ofDelaware Application June 20, 1940, Serial No. 341,513

Claims.

This invention relates to refrigeration and more Particularly to methodsand means for increasin the efliciency and capacity of refrigerationsystems by increasing the capacity andefficiency of evaporators orcoolers and condensers employed in such systems. I

The problem, in connection with refrigeration machines, of providingadequate cooler and condenser surfaces, has in the past, presentednumerof deficiency in cooler and condenser design and construction. Inactual practice, it has been customary to provide a number of tubeswithin a shell, to be used either as a cooler or condenser. Whiledifferences in function caused different shell and tube structures to beemployed, the es- 'sential difficulty was not overcome in that the useof plain tubes resulted in limiting the capacities or else caused theshell and tube structures to be inordinately large and expensive. Whilethe art appreciated that tubes might be used with fins or extendedsurface, the use of Aerofin type tubes was not satisfactory since thespaces between tubes, and the spacing on tubes, within the-limitationsof the finning process, would not result in an efficient structure.Besides, the problem of removing such finned tubes from the shells hadnot been satisfactorily solved, since the tube ends when rolled to adiameter which exceeded the tube plus fin would have thin and weak wallsoften making them unfit for further use when removed from a shell. As aresult, finned tubes have not been satisfactorily used in practice;while the use of plain tubes closely nested together has limited theefficiency and capacity of the refrigeration system in which they wereemployed.

Applicant has solved the problem by enabling the surface area in suchcoolers and condensers to be greatly increased without proportionatelyincreasing the size of the cooler and condenser shells themselves. Inaddition, applicant has provided a surface ratio between the insidesurface of a tube and the outside surface which, in combination with anovel method of stacking the tubes and inarranging the tubes in apredetermined section of a shell, results in a revolutionary increase incapacity never before achieved.

A feature of the invention covers the use of metal extruded from thesurface of a tube to provide a desired configuration on the surface ofthe tube. Such extrusion may be accomplished by apparatus disclosed, forexample, in U. S. Patent 1,865,575. This not only results in a correctratio between inside and outside tube surface, but also promotesexceedingly efficient heat exchange because the fllm resistances arereduced to a minimum. The extruded surfaces are comparatively small inheight compared to the finned surfaces heretofore produced, for example,by the Aerofin process. Consequently, applicant efficiently utilizestubes substantially of the same diameter as" the plain tubes heretoforeused and can nest them so closely together that the space in a shell isused to maximum advantage and eificiency in heat exchange greatlyincreased compared to that achieved with other types of tubes havingequal inner or outer surface areas. No previous type of tubes have beenbuilt employing equivalent inner and outer surface areas in the sametube or having equivalent inner and outer surface ratios.

The use of such tubes of small diameter closely nested together not onlyreduces the size of coolers and condensers required to produce desiredrefrigerating effect, but consequently reduces the refrigerant chargerequired. The combination of closely packed tubes, following applicantspattern of stacking and applicants surface ratios, as well asapplicantsspecification of extruded surfaces, enables submergence lossesto be held to a minimum, while at the same time permits a ratio betweenliquid and surging gas which promotes maximum effectiveness of heatexchange.

These and other advantages will be more apparent from the followingdetailed description of applicants invention, setting forth hisspecification of shell and tube structures, to be read in connectionwiththe accompanying drawings in which:

Fig. 1 illustrates diagrammatically a refrigeration system includingcooler and condenser structures incorporating applicants invention;

Fig. 2 is a sectional view of a cooler of the type used in the system ofFig. 1;

Fig. 3 is a sectional view of a condenser of the type used in the systemof Fig. 1;

Fig. 4 is a fragmentary view in section of a series of tubesillustrating the manner of stacking of the tubes in the cooler andcondenser structures of Figs. 1, 2 and 3;

Fig. 5 illustrates the interpositioning in a cooleror condenserstructure of two adjacent tubes formed in accordance with applicantsinvention;

Fig. 6 illustrates the interpositioning in a cooler or condenserstructure of two adjacent tubes formed in accordance with applicantsinvention,

in which the ends are directly soldered into a tube sheet; and

Fig. 7 illustrates two such tubes having belied ends rolled within atube sheet.

Considering the drawings, similar designations referring to similarparts, numeral l illustrates a base on which are suitably mountedcompressor ll, condenser I2 and evaporator or cooler IS.

The compressor is driven by a suitable motor, turbine or other drivingmeans, not shown, and serves to compress a suitable refrigerant, whichis discharged to condenser I2 where the refrigerant is liquefied, andthen delivered to cooler or evaporator l3 and finally returned to thecompressor in the usual refrigeration cycle. Since such cycle is Wellunderstood by those skilled in the art, no detailed description of theconstruction of the compressor and associated elements is required to anunderstanding of the invention which relates primarily to the condenserand cooler structures.

Considering cooler 13, a plurality of tubes 14 are stacked or nested inthe lower portion of shell l5. With tubes formed in accordance withapplicants invention, optimum results will be achieved if the tube nestin shell l5 extends from above refrigerant distributing plate IE to anupper tube line I! situated forty to fifty per cent of the height of theshell above the bottom there- In practice, refrigerant in liquid formenters distribution channel I8 and through spaced openings in the sidesof channel plate I6 enters the shellproper. Under load conditions, therefrigerant becomes a turbulent mixture of gas and liquid due to theheat exchange between the liquid to be cooled within the tubes I4 andthe refrigerant surrounding the tubes. The gas rising above the tubelevel line H passes through eliminators l9, where entrained liquidrefrigerant is removed, then through perforated pressure equalizationplates 20, and finally entering the compressor through suction intake 2I. The refrigerant gas, after compression, enters condenser [2 throughconduit 22, is diverted by dispersion baffle 23 and then impingesagainst the outer surfaces of tubes 24, through which a suitable coolingfluid is circulated. With tubes formed in accordance with applicant'sinvention, optimum results will be achieved if the tube nest in shell I2is positioned substantially as illustrated and lower tube line 25 islocated a distance between 60-80% of the diameter of the shell from anextremity thereof. The baffle shown located within the tube bundle inthe condenser extends about two-thirds of the distance across the shelland thereby serves to in crease the velocity of the gasv over a majorpart of the tube bundle by increasing the length of travel. The battleprovides a quiet zone there above, wherein the non-condensibles arecollected. Since turbulence and velocity are at a minimum in this upperzone, the concentration of non-condensibles therein is facilitated anddiffusion thereof mitigated.

The suction intake should be indicated by 2| instead of 20.

Baffle shown at the bottom of the condenser serves to avoid bypassing ofrefrigerant from conduit 22.

The problem in the cooler and condenser is to promote heat exchangebetween the fluid in the.

tubes and the refrigerant surrounding the tubes at a maximum rate andwith a maximum utilizationlof space and minimum refrigerant charge.

The rate of heat transfer through tubes I4 and an overall outsidediameter of 34;".

24 depends in great measure on the refrigerant film resistance. Thisresistance is radically reduced 'by applicant by providing aconcentration of surface area on the outside of the tubes so that theratio between outside tube surface area and inside tube surface area isin the neighborhood of 3.5. In addition, the stacking of tubes asillustrated in Figs. 2, 3 and 4 results in a concentration of heatexchange surface making for practical maximum efideiency. Applicant hasfound that his desired ratio of outside to inside tube surface area canbest be obtained by using a tube with an outside diameter between /8 to1" having extruded surfaces, preferably in the form of extruded finseight to forty to the inch, said extruded fins being .020" to .125" inheight. The tube ends are belied, preferably as described in copendingapplication Serial No. 340,328 filed June 13, 1940, so that the tubesare removable from the evaporator and condenser shells. In one preferredform of the invention, applicant provides a series of tubes 20, whosenominal outside diameter is /8". The thickness of the tube Wall is.049". Each of' the tubes has 16 fins to the inch, each fin being 1 6"in height making The spacing between adjacent tubes is /8" so that thetubes are interpositioned on "/8" centers. Each fin is about .020" thickat the bottom and about .010 thick at the top, although the limits offin thickness at the bottom may be between .015" to .020" while thelimits of fin thickness at the top may be between .007" to .010".

The dimensions, surface ratios, and manner of stacking tubes asaforesaid are particularly adapted for use with low pressurerefrigerants having high specific densities. However, high pressurerefrigerants will give advantageous results, under comparable operatingconditions, as for example when used to produce low temperatures as inoperations requiring below freezing conditions.

Applicant's arrangement of evaporator tubes, stacked as illustratedinFigs. 2 and 4, enables the refrigerant charge to be employed mosteffectively with submergence losses reduced to'a minimum. By utilizingan area whose upper.

level is approximately 45% of the height of the evaporator shell, thetube bundle is reduced to a practical minimum which facilitates optimumturbulence and velocity of refrigerant over the tube surfaces. Theescape of gas is very rapid and undesirable and unequal accumulations ofgas, as might be the case with a tube bundle of greater height, arereduced to a minimum.

Of further importance, applicants stacking as shown in Figs. 2 and 4prevents excessive velocities of gas through the tube bundle whichotherwise will wipe away liquid from the tube surface and reduce theheat transfer efiect.

In other words, the stacking is an important factor in promotingnecessary turbulence to produce-maximum heat exchange with minimumsubmergence losses while limiting the velocity of the gas to preventundesirable sweeping away of liquid refrigerant from the outside tubesurfaces.

The same surface ratios, extruded fin construction and stackingarrangement result in exceedingly effective condenser action too, givingmore than two and one-half times the rate of heat transfer compared toformer condenser structures employed for equivalent uses. Theutilization of tubes designed as aforesaid, in an area in the condensershell approximately 60 to 80% of the diametral height of the shellresults in speedy condensation, with the production of a gas velocitysufficient in this case to wipe away non-condensible gases from theouter surfaces of the into tube sheet 29, to facilitate replacement oftubes, whereupon the spacing between fins of adiacent tubes would beMr".

Since certain changes in carrying out the above method of operation andinthe constructions set forth, which embody the invention may be madewithout departing from its scope, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a refrigeration system of the character described, an evaporatorshell. a tube bundle with n the evaporator shell, the tubes in saidbundle having extrusions on the outer surface thereof, said extrusionsbeing in the form of fins, the ratio between the outside tube surfacearea and inside tube surface area being more than three to one, theinside cross-sectional area of the evaporator shell in wh ch said tubebundle is located being substantially forty to fifty percent of thetotal ins de cross-sectional area, means for admitting liqu drefrigerant at the bottom of the shell upwardly throu h the tube nest,and means above the tube nest for withdrawing evaporated refrigeranttherefrom for delivery from the shell.

2. In a refrigeration system of the character described, a condensershell. a tube bundle within the condenser shell. the tubes in saidbundle having extrusions on the outer surface thereof, said extrusions,being in the form of fins, the ratio between the outside tube surfacearea and inside tube surface area being more than three to one, theinside cross-sectional area of the condenser shell in which said tubebundle is located being over sixty percent of the total insidecrosssectional area, means at the bottom of the shell for removmgcondensed refrigerant from the shell, and an inlet arrangement proximatethe bottom of the shell for admitting refrigerant in gaseous form forpassage upwardly through the tubcnest. 4

3. In a refrigeration system of the character described. a shellstructure. a tube bundle within the structure. means for passing a fluidthrough the tubes. means for routing refrigerant in con-- tact with theoutside surfaces of the tubes, each tube having extended surfaces in theform of fins extruded fromand extending from the outside thereof. saidsurfaces extending approximately one sixteenth inch in height from thetube and forming an aggregate outside surface bearing a ratio withrespect to the inside surface of the tube of over two to one, said tubesbeing interpositioned in stacks between an intake opening and adischarge opening whereby a low pressure refrigerant having a highspecific density will be in turbulent condition substantially throughoutthe bundle and be substantially free of submergence losses.

4. In a refrigeration system of the character described, a shellstructure, a tube bundle within the structure, means for permitting thepassage of refrigerant upwardly in contact with the outside surfaces ofthe tubes, the tubes having extended surfaces in the form of finsextruded and extending from the outside thereof, said surfaces extendingapproximately one-sixteenth inch in height above the tube and forming anaggregate outside surface bearing a ratio with respect to the insidesurface of the tube of approximately three to one, said tubes beingstacked between an inlet adjacent the bottom of the shell and the top ofthe shell filling the greater part of the interior of the shell, thetubes being interpositioned in such manner that alow pressurerefrigerant having a high specific density may have a velocitysumciently high to sweep away non-condensible gases from the outsidesurfaces of the tubes in its passage upwardly through the tube bundle.

5. In a refrigeration system of the character described an evaporatorshell, a condenser shell, a tube bundle in each of the shells, the tubesof said bundles having extended'surfaces in the form of fins extrudedand extending from the outside thereof, a charge of low pressurerefrigerant having a high specific density within the system, individualinlet arrangements in combination respectively with said shells wherebyliquid refrigerant will be admitted into the evaporator shell upwardlythrough the bundle therein and gaseous refrigerant will be admitted intothe condenser shell upwardly through the bundle condenser shell.

therein, said tubes each having a ratio between outside and insidesurfaces thereof so that the system may operate at maximumefliciencywhen the tubes in the evaporator shell occupy substantiallyforty to fifty percent of the inside crosssectional area of theevaporator shell and the tubes in the condenser shell occupy over sixtypercent of the inside cross-sectional area of the WALTER JONES.

